For problems with accessibility in using figures
and illustrations in this method, please contact
the SLTC at (801) 233-4900. These procedures were designed and tested for internal use by OSHA personnel.
Mention of any company name or commercial product does not constitute endorsement by OSHA.

The SKC Ultra sampler was previously tested at OSHA SLTC with a mixture of
seven toxic industrial chemicals (TICs) as part of The Marines Project (Ref. 1).
The Ultra sampler is based on SKC’s 575 series of passive samplers. The Ultra
passive sampler is constructed so that the contained sampling medium can be
easily removed for analysis. This unique feature was specified by the Marine
Corps to permit analysis by thermal desorption. OSHA’s work showed that the
Ultra sampler and the associated analytical techniques worked well, but that the
Tenax TA sampling medium specified by the Marine Corps had low capacity for the
TIC mixture. The Marines had specified Tenax TA because it gave satisfactory
results for chemical warfare agents in work performed by a contract laboratory.
The Marines recognized that exposure to TICs was much more likely than exposure
to chemical warfare agents, but determination of the latter was the primary
emphasis of their program. Determination of TICs has been termed by the Marines
as the icing-on-the-cake.

This work was performed to test the sampling capabilities of Ultra samplers
containing sampling media other than Tenax TA when challenged with a mixture
containing twenty of SLTC’s most requested solvent analytes. The other
sampling media were Carboxen 1016, Carbopack Z, and Chromosorb 106. Carboxen
1016 was selected because it gave promising results when tested by Supelco to
sample a 43-component gas mixture (Ref. 2). Carbopack Z was tested because
Supelco suggested its use as a possible alternative sampling medium, and
Chromosorb 106 was tested because of personal recommendations.

REAGENTS

The solvent analyte mixture was prepared using the volumes shown in Table 1
to create the mixture.

Dodecane (99+%, Lot EI 03040LV) was purchased from Aldrich
Chemical. This material was used as an internal standard for solvent-desorbed
samples.

A solution composed of 60% DMF, 40% carbon disulfide, and 0.5 µL dodecane per
milliliter of solution was prepared to analyze solvent-desorbed samples.

SAMPLING MEDIA

The source of empty SKC Ultra Passive Sampler cases were
those used in the Marines Project. These sampler cases were each refilled with
cleaned sampling media and used in this work. Recycling Ultra samplers is
possible because the section through which the air sample diffuses is not
disturbed by either analysis or by refilling the device. A photograph of an
Ultra sampler is shown in Figure 1. The sampling medium in the vial is Tenax TA.

Carboxen 1016 was obtained from Supelco in bulk form. The lot
number was 6024355-10 and the mesh size was 60/80. This material was thermally
conditioned at 415ºC for 25 min before each use with the tube conditioning feature of the TurboMatrix
ATD. The medium was reused three to five times before it was discarded and
replaced with fresh medium.

Carbopack Z was also obtained from Supelco in bulk form. The
lot number was 0540 and the mesh size was 60/80. This material was thermally
conditioned at 415ºC
for 25 min before each use with the tube conditioning feature of the TurboMatrix
ATD. The medium was reused three to five times before it was discarded and
replaced with fresh medium.

Figure 1. SKC Ultra Passive Sampler.

Carbopack Z was also obtained from Supelco in bulk form. The
lot number was 0540 and the mesh size was 60/80. This material was thermally
conditioned at 415ºC
for 25 min before each use with the tube conditioning feature of the TurboMatrix
ATD. The medium was reused three to five times before it was discarded and
replaced with fresh medium.

The source of Chromosorb 106 was SKC Catalog No. 226-110,
20/40 mesh size, Lot No. 1066, sampling tubes. This medium was thermally
conditioned at 250ºC
for 25 min before each use with the tube conditioning feature of the TurboMatrix
ATD. The medium was reused three to five times before it was discarded and
replaced with fresh medium.

SKC Ultra samples were thermally desorbed using a Perkin Elmer TurboMatrix
ATD (equipped with internal standard addition option) connected to the
electronic-pressure controlled volatiles interface inlet of an Agilent 6890
Series GC system and an Agilent 5973 Network Mass Selective Detector (MSD). The
ATD and GC carrier gas was helium. Each sample was desorbed two times to confirm
that desorption was complete. ATD conditions: Thermal desorption tubes
containing Chromosorb 106 were desorbed at 240ºC
for 9 min following a 1 min purge. Tubes containing Carboxen 1016 and Carbotrap
Z were desorbed at 415ºC
for the same times. The focusing trap was flash heated from -30ºC
to 300ºC and
maintained at the upper temperature for 2 min. The two-section trap contained
14-mm Tenax TA and 6-mm Carbopack B positioned so that the desorption flow first
passes through the Tenax TA section. The GC transfer line temperature was 225ºC
and the valve temperature was 225ºC.
The inlet split flow was 28 mL/min, the desorb flow was 58 mL/min, the internal
standard tube load flow was 23 mL/min, and the internal standard loop flow was
1.3 mL/min. GC conditions: A HP-5MS capillary GC column (30-m × 0.25-m i.d. ×
1.0 µm df) was used
for this work. The GC column was temperature programmed from 40ºC
(following a 1 min hold) at 10ºC/min
to 200ºC. The GC
column was operated in the constant flow mode at 0.8 mL/min. The GC inlet
temperature was 230ºC,
and the inlet splitratio was 67 to 1. MSD conditions: thermal auxiliary 2 was
280ºC, MS source was
230ºC, MS quad was
150ºC. The MSD was
operated in the full scan mode from 24 to 350 AMU. EM voltage was automatically
set by the MSD software via an "autotune" performed every week of
operation. Typically, a solvent delay of 2 min was employed.

SKC CMS samples were analyzed after desorption with one
milliliter of 60/40 DMF/carbon disulfide mixture (containing 0.5 µL/mL
dodecane internal standard) for one hour using a HP 5890 GC equipped with a
Restek Stabilwax capillary column (60-m × 0.32-m i.d. × 1.0 µm
df), an automatic liquid injector, and an FID. The GC column was temperature
programmed from 40ºC
(following a 1 min hold) at 6ºC/min
to 190ºC. The FID
was maintained at 250ºC and the injector at 220ºC.
The GC column flow was 4.0 mL/min hydrogen. The inlet split ratio was 50 to 1.
The FID gases were 35 mL/min hydrogen, 415 mL/min air, and 30 mL/min nitrogen
(auxiliary).

Humid air (for use with controlled test atmospheres) was
generated using a Miller-Nelson Model HCS 501 Flow-Temperature-Humidity Control
System. This system was equipped with a 500 L/min mass flow controller.

Relative humidity and temperature of the test atmospheres
were monitored with a Omega Digital Thermo-Hygrometer meter and probe The probe
was calibrated by the manufacturer. Pressure within the exposure chambers was
monitored with an Omega meter and pressure transducer that was calibrated to
read ambient barometric pressure for a fully vented exposure chamber before each
run.

Dilution air flow rates (50-360 L/min) were measured with a
Equimeter No. 750 gas meter. The meter readings for several different flow rates
were compared to those of a Singer DTM 115 gas meter (which had been tested by
the local natural gas distributor and found to be accurate) that was connected
in series before the Equimeter. Both meters gave very similar readings.

The solvent mixture was metered into the system with an Isco
100 DM syringe pump equipped with a cooling/heating jacket and an insulation
cover package. The pump was operated in the constant flow mode. The temperature
of water in the cooling/heating jacket was maintained at 23ºC with a Forma Scientific Model 2006 CH/P Bath and Circulator.

Solvent vapors were generated by pumping the liquid into a
vapor generator where it evaporated into the dilution air stream. The vapor
generator consisted of a 10-cm length of ¼-inch o.d. glass tubing with a small
hole in the side. The hole was just large enough for 1/16-inch
o.d. tubing to be inserted. The glass tubing was placed inside a ½-inch
stainless steel Swagelok tee wrapped with heating tape. The 1/16-inch
tubing entered the third port of the tee through an adaptor and was inserted
about 1/8 inch (approximately in the center) into the glass tubing through the small hole.
Solvent was pumped through the tubing and into the glass tubing. The liquid flow
rate was slow enough (about 10 µL/min)
so that liquid did not accumulate in the evaporation tube. The entire dilution
air stream passed through the tee and swept generated vapors into the apparatus.

The following is a description of the arrangement of the apparatus that was
placed in a walk-in hood (Figure 2). Liquid from which vapors were to be
dynamically generated was pumped with a precision Isco syringe pump (an
identical pump and a small solvent mixing tee was available when its use was
desired) into a heated manifold where it evaporated. The generated vapors were
swept from the manifold with dilution air. Stainless steel tubing (½-inch o.d.)
connected with stainless steel Swagelok fittings was used to transfer the test
atmosphere. The dilution air was humidified using a Miller-Nelson
Flow-Temperature-Humidity controller. The vapor/dilution air mixture then passed
into a 3×24-inch stainless steel mixing chamber. The test atmosphere next
passed through ½-inch ball valves where it could be either diverted to waste,
or directed into the exposure chamber. An additional ball valve allowed the
chamber to be purged with room air. The transfer tubing diameter was increased
from ½ inch to 1 inch at this point using a Swagelok adaptor attached to the
chamber inlet. Tube and fitting diameter was increased to 1 inch after this
fitting to help reduce any increased pressure to ambient. The 1-inch o.d.
chamber inlets have small stainless steel deflectors to help insure that the
test atmosphere completely fills the sampling chamber. Stainless steel screens
were placed inside the chamber for the same purpose.

Figure 2. Sample exposure apparatus with small exposure chamber.

This design should cause
air flow through the chamber to be somewhat turbulent. Face velocities of the
test atmospheres were calculated by dividing the volumetric flow of each
atmosphere by the cross-sectional area available for air flow in the chamber.
The cross-sectional area available for air flow was the cross-sectional area of
the chamber reduced by the cross-sectional area of the sampler. The exposure
chamber is used with a removable door (that is not shown in the photograph) to
completely seal it when used with test atmospheres. Test atmospheres exit
through a stainless-steel manifold connected in-line to permit collection of
active samples.

EXPERIMENTAL

Preparation of Samples

Ultra Passive Samplers were prepared for analysis by prying open the back of
the sampler with a screwdriver to reveal the end of the built-in aluminum funnel
containing the sorbent. The sampling medium was then carefully transferred into
the back of a clean, empty Perkin-Elmer thermal desorption tube using the
funnel. The front of a thermal desorption tube is the end with the groove and
the back is the opposite end. A gauze screen was then carefully placed on top of
the sampling medium with the aid of a 3/16-inch glass rod
and a small screwdriver. The gauze screen can be inserted easier if its concave
side is placed so that it faces towards the back of the tube. The tube was not
completely filled with the sorbent and an empty space of approximately ½ inch
remained in the end of the tube. A retaining spring was then placed into this
space at the end of the tube, and then seated on top of the gauze screen
slightly below the end of the tube using the funnel.

CMS active sampling tubes were prepared for analysis by placing each section
of sorbent into separate 2-mL automatic sampler vials and then adding 1 mL of
60/40 DMF/carbon disulfide desorbing solution. These vials were allowed to stand
one hour, and were shaken by hand several times during this time.

Analytical Standards

Analytical standards for thermally-desorbed samples were prepared by spiking
5-µL aliquots of a
series of diluted solvent analyte mixtures onto the front of thermal desorption
tubes containing the appropriate sampling medium. Room air was drawn air through
these tubes at 50 mL/min for about 10 seconds immediately after they were
spiked. The source of the thermal desorption tubes was Ultra samplers that had
been previously analyzed, and then reconditioned for 25 min at the appropriate
temperature using the thermal desorber tube conditioning feature. These thermal
desorption tubes were reused no more than three to five times before recycling.
Recycling thermal desorption tubes was accomplished by removing the retaining
spring, the gauze screen, and the sorbent from previously analyzed samples. The
empty tubes were washed twice with methyl alcohol and then air-dried overnight
before reuse.

Analytical standards for solvent-desorbed samples were prepared by injecting
microliter volumes of diluted solvent analyte mixtures into the same volume of
60/40 DMF/carbon disulfide desorption solution used to desorb the samples

Analytical Instrument Calibration

GC/MSD calibration curves were prepared for each analyte with a series of
standards using the MSD software. The calibration range, in most cases, was
one-half to two times the expected sample concentration. All calibration curves
were linear. The MSD is saturated at approximately 50 ng per analyte. A
combination of GC injector split and/or TD split should be employed to reduce
mass reaching the MSD when samples exceed this level. Alternatively, MSD EM
voltage can be reduced to decrease response. All MSD results were calculated
without internal standard correction.

Similar calibration curves were prepared for samples analyzed by GC/FID using
a Waters Associates Millennium Chromatography Manager data system to measure FID
response. An internal standard was employed in these analyses.

Desorption Efficiency

Solvent-desorbed samplers were used in this work to monitor concentrations of
test atmospheres. Desorption efficiency studies were performed using both wet
and dry CMS sampling medium. Wet samplers were prepared by drawing clean, 80%
humid air through the samplers at 0.05 L/min for 4 hours. Dry medium was as
contained in sampling tubes.

Sampling Rate and Capacity

Sampling rates for the CMS active sampling tubes were 0.05 L/min, and these
samples were collected simultaneously with diffusive samples. Methylene chloride
was the only mixture component found on the sampling tube backup section.
Five-percent breakthrough occurred after sampling for about 18 hours.

Sampling rates were determined at ambient temperature and pressure, but all
sampling rates presented in this work are expressed at 760 mmHg and 25ºC.
Three samplers for each sampling medium were exposed to controlled-test
atmospheres for increasing time periods for these experiments. Samples were
removed at the end of each time period and analyzed. The exposure times ranged
from two to thirty-one hours for Carboxen 1016 and for Chromosorb 106. Sampling
times for Carbopack Z were eight to twenty-two hours. The relative humidity of
the test atmospheres was approximately 80% at ambient temperature and pressure.
The face velocity of test atmospheres through the small exposure chamber was
approximately 0.4 m/sec. The theoretical concentration of each solvent analyte
in the test atmospheres was approximately 4.5 mg/m3. Sampler
orientation was parallel to the flow direction of the test atmosphere. Four
active samples were taken simultaneously with diffusive samples for each time
period. Theoretical concentrations were used to calculate sampling rates because
active-sampling results were near 100%.

RESULTS and DISCUSSION

Desorption Efficiency

The medium contained in active sampling tubes is often desorbed with 99/1
carbon disulfide/DMF solution at SLTC. It has been observed that desorption
efficiencies are low for water-soluble analytes from wet sampling medium using
this technique (Ref. 3). The reason for low recovery is that water-soluble
analytes can partition into the water phase of the two-phase solutions that
frequently occur when atmospheric water is collected (and desorbed) along with
the analytes. A 60/40 mixture of DMF/carbon disulfide was used in previous work
(Ref. 3) to prevent two-phase solutions and its use was again tested here.

The desorption efficiency for styrene was not constant over the studied
concentration range. The same inconsistency has been observed in other work by
other researchers (Ref.4).

Thermal-desorption efficiency experiments were not performed because
TurboMatrix ATD conditions were selected so that the desorption process was
essentially complete after one run. Two runs were always conducted to confirm
that desorption was complete.

Sampling Rate and Capacity

Results in the following tables are the average of three individual samplers,
and the experimental sampling rates at ambient conditions were converted to
their equivalent at 760 mmHg and 25ºC.
Sampling rates of zero mL/min mean that no analyte was detected in the sample.

Sampling times less than eight hours were not performed with
Carbopack Z because it did not arrive at SLTC until this work was well underway.
Its use was discontinued when it was found that its sampling capacity was
inadequate for the more volatile components of the solvent analyte mixture.

Sampling rate and capacity work with Chromosorb 106 was performed after it was
found that Carboxen 1016 and Carboback Z did not have sufficient sampling
capacity for many of the volatile solvent analytes of interest to OSHA.

Graphed sampling rate and capacity data are shown in Figures 3 through 63.
Sampling capacity for diffusive samplers is exceeded when the calculated
sampling rate rapidly decreases. Two horizontal lines were constructed in some
of the figures and used to estimate maximum sampling time when a sampling medium
was judged to have sufficient capacity. The lines represent the average sampling
rate ±10%. The point that the plotted data intersected the lower line was used
as an estimate exceeded sampling capacity. Obviously, sampling capacity was not
exceeded if the plotted data did not intersect the lower line.

Average sampling rates are shown in Table 6. The average was calculated using
the last tested time (samp time) before sampling capacity was exceeded as shown
in Figures 3-62. The two-hour sampling time was not included in the undecane
average for Chromosorb 106. An average sampling rate and a RSD for the
individual sampling rates was calculated for each medium. A pooled RSD was also
calculated for the RSDs for each medium. The individual RSDs for each medium
were homogeneous by the Cochran Test at the 95% confidence level. NA means not
applicable.

Table 6
Average Sampling Rates

medium

Carboxen 1016

Carbopack Z

Chromosorb 106

analyte

samp time (hours)

samp rate (mL/min)

RSD

samp time (hours)

samp rate (mL/min)

RSD

samp time (hours)

samp rate (mL/min)

RSD

IPA

NA

NA

NA

methylene chloride

NA

NA

NA

MEK

NA

NA

12

14.59

13.93

ethyl acetate

NA

NA

12

13.59

10.22

1-butanol

7

12.47

11.32

NA

16

14.44

10.26

benzene

8

14.14

10.48

NA

12

14.87

11.01

PGME

8

12.31

6.17

NA

16

13.76

8.72

heptane

31

12.78

6.93

22

11.83

7.65

31

12.95

7.60

trichloroethylene

8

12.90

7.47

10

11.25

9.98

24

11.60

9.27

MIBK

24

13.04

7.68

22

11.85

9.80

31

13.36

8.06

toluene

31

14.23

7.82

22

12.82

7.61

27

14.15

8.83

butyl acetate

31

12.59

7.08

22

11.98

3.31

31

13.10

6.13

tetrachlorethylene

31

12.97

7.18

22

11.47

10.46

27

12.34

6.58

m-xylene

31

13.85

5.90

22

12.59

7.48

31

13.68

5.99

2-heptanone

31

13.13

6.93

22

12.35

5.90

31

13.84

5.50

styrene

31

13.92

5.51

22

13.11

7.19

31

10.54

10.27

butyl cellosolve

31

12.13

10.72

22

12.26

5.86

31

12.97

4.61

TMB

31

12.85

5.80

22

11.92

7.51

31

13.03

4.18

limonene

31

12.78

8.98

22

12.85

8.55

31

11.69

5.47

undecane

31

10.95

4.84

22

10.83

7.83

31

10.41

5.71

average

12.94

12.09

13.05

RSD

6.42

5.52

9.92

pooled RSD

7.78

7.84

8.30

CONCLUSIONS

Results of this work shows some of the limitations of diffusive sampling and
of thermal desorption. Thermal desorption permits use of mass spectrometry to
identify and to quantitate sample components. This technique is extremely
sensitive because the entire sample can enter the mass spectrometer. Obviously,
the sample cannot be reanalyzed because it is entirely consumed. Sampling media
must be relatively weak to permit thermal desorption because heat cannot
effectively desorb many chemicals from strong media such as charcoal. Sampling
media used with thermal desorption generally has unsatisfactory sampling
capacity for comparatively volatile chemicals. One reason for poor capacity in
diffusive sampling is reverse diffusion. A chemical reaching the surface of the
sampling medium can migrate further into the medium and be retained, or can
diffuse off the sampler and be lost. The usual cause of reverse diffusion is use
of an inappropriate sampling medium.
Inspection of the sampling rate and capacity figures shows that none of the
tested media gave entirely satisfactory sampling performance. Chromosorb 106 had
slightly more sampling capacity than Carboxen 1016. Carbopack Z was difficult to
work with, and its capacity was inferior to Carboxen 1016 for the more volatile
components of the solvent analyte mixture. Precision of sampling rates was
similar for all three media within their respective effective sampling
capacities. All three media presented substantial artifact backgrounds for blank
samplers. This background could cause very low level analyses to be difficult.
Chromosorb 106 was judged to provide the best overall sampling results of the
three tested media. SKC Ultra samplers containing Chromosorb 106 were shown to
be an effective means to sample the solvent analyte mixture with exceptions of
IPA, methylene chloride, and perhaps MEK. It is anticipated that this sampler
could be used to develop a new fully-validated OSHA method that would find its
best application in low-level, long-term workplace sampling.